If you remember I found that the bores were in bad condition. The first port of call was to find someone who could be reliably trusted to bore out these blind cylinders. I spoke to Steve Slocombe who kindly put me in touch with the guy that he uses, the only downside was that he was 250 miles away.
I also spoke to someone more local who came recommended so I went to him.
The first thing he noticed was that my cylinders had been relined previously. This must have been done some time prior to 1936 which is the last time the bike was on the road. I left the cylinders with him and to cut a long story short it turned out that the existing liners have cleaned up nicely. As well as the scores and pitting the bores were also oval. No wonder it ran like a smoke machine. I have been told though that the previous lining job was actually very good. There are still some marks at the very bottom of the bores but they are below the rings so it is not a concern.
After a debate and lots of thought about new pistons, I decided to go with new cast iron pistons so I spoke to another specialist also reasonably local to me who could cast them for me. I picked the pistons up just before Christmas. Here is a picture of the new piston castings, one old piston and the core box and pattern.
Here is a close up of one old piston next to a new casting. Somewhere inside the one of the left is something that looks like the one on the right.
I would have quite liked to have machined the pistons myself but 2 things put me off. One, I would have been really annoyed if I had made a mistake. Two, my milling machine isn’t functional at the moment so I don’t actually have the equipment available to do them. Therefore I got someone to machine them for me. I have used a more modern style plain cast iron rings which have been kept high to make sure that they avoid any of the remaining few marks at the bottom of the bore.
I picked the pistons and cylinders up this morning (14th April 17)
Once I knew that the pistons were done I knew that the next job was balance hence my post over in the Engine section.
I deliberately hadn’t pulled the bottom end apart until the pistons were done so that the disassembly will still be reasonably fresh in my mind when I go to re-assemble it. One evening this week I reduced it from one lump into lots of bits.
That brings things up to date. Whilst that is happening I need to find someone to machine the cylinders to accept new exhaust valve guides because the new valves are at best a rattle fit in the old integral guides.
I do have a couple of other jobs to do which I had delayed until I had the engine work in hand so hopefully everything will come together in time to get some miles on the bike in the not too distant future.
Watch this space.
John
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